1. Field of the Invention
The present invention relates to a method for a time-division duplexing (TDD) system and related communication device, and more particularly, to a method of handling uplink/downlink configuration for the TDD system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Different from the LTE/LTE-A system operating in a frequency-division duplexing (FDD) mode (or simply FDD system), transmission directions of subframes of a frequency band in the LTE/LTE-A system operating in a time-division duplexing (TDD) mode (or simply TDD system) may be different. That is, the subframes in the same frequency band are divided into UL subframes, downlink (DL) subframes and special subframes according to the UL/DL configuration specified in the 3GPP standard.
FIG. 1 is a table 102 of the UL/DL configurations with subframes and corresponding directions. In FIG. 1, 7 UL/DL configurations are shown, wherein each of the UL/DL configurations indicates a set of transmission directions (hereinafter, directions, for short) for 10 subframes, respectively. Each subframe is indicated by a corresponding subframe number (i.e., subframe index) in FIG. 1. In detail, “U” represents that the subframe is a UL subframe where UL data is transmitted, and “D” represents that the subframe is a DL subframe where DL data is transmitted. “S” represents that the subframe is a special subframe where control information and maybe data (according to the special subframe configuration) are transmitted, and the special subframe can also be seen as the DL subframe in the prior art. Note that the eNB may configure a UL/DL configuration to a UE via a higher layer signaling (e.g., System Information Block Type 1 (SIB1)) or a physical layer signaling (e.g., DL control information (DCI)). The UE applies the UL/DL configuration to communicate with the eNB. That is, the UE considers a subframe as an UL, DL or special subframe according to the UL/DL configuration. The UE receives in DL subframes and/or special subframes, and transmit in UL subframes.
In an example, the UL/DL configuration 1 is configured to a UE via system information (e.g. SystemInformationBlocktype1) from a cell of an eNB. In this example, the UE supports enhanced interference management & traffic adaptation (eIMTA) and the cell configures the UL/DL configuration 4 (e.g. via a physical downlink control channel (PDCCH) or an enhanced PDCCH (EPDCCH)) to the UE according to rapid changes of traffic loads on the UL and the DL. After a while, the cell indicates the UL/DL configuration 2 according to long term changes of traffic loads on the UL and the DL. In such a condition, if the UE supporting the eIMTA remains applying the UL/DL configuration 4, the UE cannot receive the PDCCH in the subframe 3. Further, the UE also cannot transmit a physical uplink shared channel (PUSCH) in the subframe 7 even if the UE receives a UL grant for transmitting the PUSCH in the subframe 7.
In another example, a cell of an eNB indicates the UL/DL configuration 1 to a UE supporting the eIMTA via the SystemInformationBlocktype1 and configures the UL/DL configuration 4 to the UE via the PDCCH or the EPDCCH according to the rapid changes of traffic loads on the UL and the DL. Under a condition that a radio link failure occurs in the UE and the UE performs a radio resource control (RRC) reestablishment procedure to recover the radio link, the UE would keep applying the UL/DL configuration 4 since the UE is in an RRC connected mode when performing the RRC connection reestablishment procedure. In this example, the UE may select another cell configuring the UL/DL configuration 2 in the SystemInformationBlocktype1. When the UE transmits a preamble to the cell for performing the RRC connection reestablishment procedure and the cell feedback a random access response in the subframe 3, the UE cannot receive the random access responses transmitted in the subframe 3 since the UE regards the subframe 3 as the UL subframe. In such a condition, the RRC re-establishment procedure may fail.
As can be seen from the above, the inconsistency between the UL/DL configurations indicated in the system information and on the DL channel (e.g. a PDCCH or an EPDCCH) for the UE supporting eIMTA is an important issue to be discussed.